Expression of retinoid X receptors in P19 embryonal carcinoma cells and embryonic stem cells.

The pluripotent mouse embryonal carcinoma cell line P19 provides an excellent model system to study the mechanisms by which retinoic acid (RA) exerts its biological effects. When aggregated and exposed to low concentrations of RA, P19 cells differentiate into neuron- and glial-like cells. The diverse biological effects of RA are mediated by two families of receptors localized in the cell nucleus, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs). Each family consists of three members designated alpha, beta and gamma. While the patterns of expression of the RARs have been studied in P19 cells, similar data for the RXRs have not been available. We demonstrate here that these receptors are expressed in P19 and are regulated during RA-induced differentiation. We also show that pluripotent mouse embryonic stem cells express the RXRs as well.